A toothbrush of the kind described is known from WO 01/19281 A2, according to which an approximately round bristle cluster is drivable in a rotary oscillating manner. A bristle holder that is rotatably arranged in the brush head is coupled to a transmission member, which is driven back and forth lengthwise by a crank that is attached to a gearwheel. However, a crank drive of such kind has a relatively large space requirement. Moreover, because of the components it requires, it is complex and expensive. Thus, it is only practical for use in highly priced toothbrushes.
An electric toothbrush in which the rotary drive motion of the motor is transmitted to the bristle holder by a transmission member is known from U.S. Pat. No. 4,149,291. This transmission member is eccentrically coupled to the drive shaft at one end, and is supported by a ring bearing at its other end, where it exits the handpiece, so that it describes a conical driving motion. In order to impart a special, approximately elliptical motion to the detachable brush element that is seated on the transmission member, the transmission member includes a spring that flexes along one axis. As a result the conical driving motion of the transmission member is only transferred to a limited degree in this one axis. However, because of the sophisticated design of the transmission member, this drive is complicated and expensive. Additionally, because of its spring-driven configuration, it is prone to fatigue. Moreover, the elliptical drive motion of the toothbrush head is in many respects disadvantageous.
German Patent No. DE 20112320 U1 describes another electric toothbrush, in which the brush holder, with the bristle cluster affixed thereto, is arranged rigidly at one end of a drive rocker, which is disposed inside a hollow brush handle. The drive rocker is arranged to rock in multiple axes and is excited to oscillate in two axes by piezoelectric elements that are arranged at the other end of the drive rocker, between the rocker and the internal wall of the brush handle. However, the bristle holder, which is securely affixed to the rocker end, performs only relatively small, tethered movements. Particularly, rotating movements that turn the bristle cluster in on itself cannot be performed to a degree that would yield an optimum result in terms of cleaning the teeth.